1. Field of the Invention
The present invention relates to colored sintered bodies of aluminum nitride and, more specifically, to sintered bodies of aluminum nitride which have a high density, a high thermal conductivity and a desired color, such as brownish black, brown, green, etc.
The present invention further relates to circuit boards and packages including semiconductor devices in which sintered bodies of aluminum nitride above mentioned are employed. 2. Description of the Prior Art
In recent years, there has been a remarkable progress in large scale integration (LSI) technology and considerable improvements have been made in the integration techniques.
Improvements in size of integrated circuit (IC) chips contribute to such recent LSI innovations. As the size of IC chips has been increasingly improved, generation of heat for each package also becomes larger. Accordingly, the heat dissipation property of substrate materials has become increasingly important. Heretofore, sintered alumina has been employed as an IC substrate material. However, since the thermal conductivity of the sintered alumina is not sufficient for permitting satisfactory heat release, the conventional sintered alumina can not provide satisfaction for such increasing heat generation of IC chips. For this, beryllia having a high thermal conductivity has been studied as a substitute for the sintered alumina substrate, but it is difficult to handle because of its strong toxity.
Sintered aluminum nitride (AlN) has become of interest as substrate materials for circuit boards and packaging materials in the semiconductive industry, because it inherently has a high thermal conductivity and a high electrical insulating property and is nontoxic.
As set forth above, aluminum nitride has a high thermal conductivity and a good insulating property in the state of single crystal. However, in case where sintered bodies are prepared from aluminum nitride powder by compression-molding followed by sintering, the resultant sintered bodies, although depending on sintering conditions, exhibit a low relative density i.e., at most, of the order of 70 to 80% (based on theoretical density of 3.26 g/cm.sup.3 of aluminum nitride) and include a large number of pores, because of poor sinterability of aluminum nitride powder per se.
The mechanism of heat conduction of insulating ceramics, like aluminum nitride, is mainly based on transmission of phonons. However, since the defects due to pores, impurities, etc., of the ceramics may cause phonon scattering, actually there can be obtained only sintered bodies of aluminum nitride having a low heat conduction level. Under such circumstances, many methods have been proposed to achieve aluminum nitride sintered products having a high thermal conductivity.
However, in order to produce aluminum nitride sintered products of high thermal conductivity, highly pure raw materials should be employed and inclusion of impurities which may be caused during the production process should be held as small as possible. Sintered products of aluminum nitride obtained in such conditions are limited to white transparent products or faintly colored products. There have not been yet obtained colored sintered products of aluminum nitride having a high thermal conductivity. Accordingly, it is highly desirable to develop colored sintered bodies of aluminum nitride for applications where light-transmitting properties are considered as an important matter.